An optical measuring device for measuring surfaces is known from publication DE 10 2008 041 062 A1. The known measuring device produces a measuring light beam which, after passing through at least three separately focussing optical components, impinges on the surface of the object, is reflected by it and is detected by a spatially resolving light detector together with a reference light following interferential superposition.
To achieve this the known measuring device has an optical assembly which comprises the at least three separately focussing optical components. The main axes of these separately focussing optical components are positioned offset in relation to one another and side by side. In addition, the known measuring device has a beam splitter positioned in a beam path of the measuring light beam. Furthermore, a reference face and a spatially resolving light detector are provided for the known device.
The light source, the beam splitter and the optical assembly are positioned in relation to one another so that measuring light emitted by the light source and passing through the focussing optical components impinges on the surface, is reflected by it and impinges on the detector via the focussing optical components. In addition, the known measuring device has an evaluation system for receiving image data from the spatially resolving light detector and outputting measurement data which represents a surface shape of the surface. To do this distance values representing a distance between a location on the surface and the focussing optical components are acquired. From these distance values the evaluation system forms parameters which represent the surface shape of the surface.
In addition, the above publication discloses a method for measuring a surface of an object comprising essentially the following steps. First, a measuring light is produced. From this measuring light are formed three converging partial beams of a first part of the measuring light to light three regions of the surface of the object which are positioned a certain distance apart. The reflected light, or the three partial beams of the light reflected by the surface, are directed together with a second part of the measuring light towards a spatially resolving detector where they form interferences. Finally, these interferences are analysed by a detector that detects light intensities in order to represent the surface shape of the surface of the object by corresponding measurement data.
Further known methods are specified in publication DE 10 2008 041 062 A1, U.S. Pat. No. 7,826,068 B2, US 2009/0078888 AS1, WO 2013/070732 A1, U.S. Pat. No. 7,853,429 B2, U.S. Pat. No. 7,443,517 B2, DE 10 2011 081 596 A1, DE 10 2011 055 735 and KR 10 2008 0112436.
The measuring of stages between a rotating support and a rotating edge region of an object to be measured, in particular an object to be thinned, requires a robust measuring device which occupies a limited amount of space while withstanding high environmental pollution.
For this reason conventional, robust stage measuring devices continue to operate with tactile probes, one probe scanning the surface of a narrow exposed edge region of the object to be measured and a second probe positioned on the upper face of the rotating support so that the stage height from the millimeter range to the multiple micrometer range which arises during machining can be acquired from the acquirable distances between the two probes. One difficulty of such tactile measuring methods lies in the appropriate dosing of the pressing force on the edge region of the object to be measured on one hand and on the surface of the support material on the other.
If the pressing force is too high, the possibility of damage to the edge regions of the object to be measured cannot be excluded, especially since a multiplicity of grinding rotations of the object is required to thin the object from a thickness in the millimeter range to thicknesses of below 100 micrometers. If the pressing force is too low, interference occurs because the probes are exposed to considerable measuring errors and measurement inaccuracies at least on the relatively rough upper face of the support as a result of grinding particles occurring during thinning.